Compositions for electric field grading

Abstract

Compositions comprising ferrosoferric oxide dispersed in a polymer matrix. Such compositions may exhibit properties suitable for achieving both resistive field grading effects and capacitive field grading effects e.g. in electrical stress control devices and surge arrestor devices. Such compositions may optionally include one or more capacitive field grading additives and/or conductive additives.

What is claimed is: 
     
       1. A electric field grading composition comprising a particulate ferrosoferric oxide material dispersed in a polymer matrix and having a dielectric constant between about 10 and about 20 as measured at a frequency within the range of 10 kHz to 500 kHz, wherein the electric field grading composition exhibits a reversible non-linear current-voltage relationship. 
     
     
       2. The composition of  claim 1  wherein the ferrosoferric oxide material is undoped. 
     
     
       3. The composition of  claim 1  wherein the ferrosoferric oxide material comprises between about 15 volume % and about 45 volume % of the composition. 
     
     
       4. The composition of  claim 1  having a loss tangent of about 0.05 or less at a frequency of 10 kHz at room temperature. 
     
     
       5. The composition of  claim 1  wherein the polymer matrix comprises material selected from the group consisting of thermoplastic materials, thermosetting materials, gels, and greases. 
     
     
       6. The composition of  claim 1  wherein the polymer matrix comprises polymers selected from the group consisting of: silicones; epoxies; ethylene-propylene-dienes; polyolefins; polyurethanes; epichlorohydrins; fluoroelastomers; and copolymers, blends and/or mixtures thereof. 
     
     
       7. The composition of  claim 1  further comprising a capacitive field grading particulate additive. 
     
     
       8. The composition of  claim 7  wherein the capacitive field effect particulate additive is chosen from the group consisting of TiO 2 , CaTiO 3 , SrTiO 3 , BaTiO 3 , BaSrTiO 3 , SrTiO 3 , PbTiO 3 , Pb[Zr x Ti (1-x) ]O 3 , and x[Pb(Mg 1/3 Nb 2/3 )O 3 ]-(1−x)[PbTiO 3 ]. 
     
     
       9. The composition of  claim 1  further comprising a conductive particulate additive. 
     
     
       10. The composition of  claim 9  wherein the conductive particulate additive exhibits an aspect ratio of at least about 10:1. 
     
     
       11. The composition of  claim 1  wherein the conductive particulate additive comprises graphene. 
     
     
       12. An article comprising the composition of  claim 1 . 
     
     
       13. The article of  claim 12  wherein the article is a surge arrestor. 
     
     
       14. The article of  claim 12  wherein the article is an electrical stress control article. 
     
     
       15. The article of  claim 12  wherein the article is a high voltage cable splice. 
     
     
       16. The article of  claim 12  wherein the article is a high voltage termination. 
     
     
       17. A method of forming an article, the method comprising: combining ferrosoferric oxide particles with a polymeric material to form a composition that exhibits a dielectric constant between about 10 and about 20 as measured at a frequency within the range of 10 kHz to 500 kHz and that exhibits a reversible non-linear current-voltage relationship, and shaping the composition into an article. 
     
     
       18. The method of  claim 17  wherein the article is a surge arrestor. 
     
     
       19. The method of  claim 17  wherein the article is an electrical stress control article. 
     
     
       20. A method of performing electrical stress control, the method comprising positioning an article comprising the composition of  claim 1  in proximity to an electrical cable. 
     
     
       21. A electric field grading composition comprising a particulate ferrosoferric oxide material dispersed in a polymer matrix, wherein the electric field grading composition exhibits a reversible non-linear current-voltage relationship, and wherein the composition further comprises a conductive particulate additive comprising graphene. 
     
     
       22. An article comprising the composition of  claim 21 .